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Antarctic meltwater discharge has been largely emphasized for its potential role in climate change mitigation, not only by reducing global warming, but also by stabilizing the Atlantic Meridional Overturning Circulation (AMOC). Despite the tremendous impact of the AMOC on the climate system, its temporal evolution in response to the meltwater remains poorly understood. Here, we investigate the meltwater impacts on the AMOC based on the GFDL CM2.1 experiments and discover its fast weakening and slow strengthening to the Antarctic meltwater discharge. Cold ocean surface caused by meltwater spread throughout the globe and eventually strengthened the AMOC. However, in the early stages, the tropical temperature response could stimulate the Rossby wave teleconnection, modulating atmospheric circulation in the North Atlantic, and weakening convection and even the AMOC. This counterintuitive evolution implies a potential destabilizing effect of Antarctic meltwater, underscoring the importance of the atmospheric dynamics in the interaction between the two poles. Plain Language Summary: The climate system is made up of interactions between different subsystems, so that regional climate changes can have global effects. The freshwater discharge from Antarctica would increase in the future and result in regional cooling. Atmospheric and oceanic dynamics extend this local effect to the globe, reducing global surface temperature and strengthening the large‐scale ocean circulation in the Atlantic. These mitigating effects naturally put the spotlight on Antarctic meltwater. Our study however suggests that the mitigation effect depends on the time scale. Although the global mean temperature is always reduced, the ocean circulation in the Atlantic surprisingly slows down as an early response to Antarctic meltwater; fast atmospheric teleconnection enables it. This non‐monotonic evolution emphasizes the importance of the atmospheric teleconnection between the two poles, which should be carefully considered to understand the polar climate. Key Points: The response of the Atlantic Meridional Overturning Circulation to perennial meltwater‐induced cooling is investigated by GFDL CM2.1 experimentsBefore the cooling spreads out the Atlantic, tropical atmospheric teleconnection could weaken the Greenland ocean convectionThe fast and slow responses imply the importance of the atmospheric teleconnection to regulate polar climate [ABSTRACT FROM AUTHOR]

The synoptic cold surge is a weather event that frequently occurs in the Northern Hemisphere, often causing severe damage accompanied with intense winds and precipitation. It is reported that the Arctic Oscillation and the North Atlantic Oscillation can affect the cold surge. However, on interacting with tropical circulation, the cold surge potentially links to the Antarctic sea‐ice loss with influence extending to Tropics. Therefore, this research aims to investigate the potential link between Antarctic sea‐ice loss and Northern Hemisphere cold surges and corresponding wind–precipitation compound events. To study this link, twin numerical experiments using a physically based atmosphere model with a prescribed 30% Antarctic sea‐ice loss scenario were used. The results show that the cold surge occurs more frequently in most regions of the world, except for central North America and central Eurasia. In Europe, the cold surges occur closer to the lower latitudes in the Antarctic sea‐ice loss scenario. Additionally, the Antarctic sea‐ice loss can result in intensified wind and precipitation extremes within compound events. The intensified precipitation extremes are caused by increased moisture transportation by tropical easterlies and higher local temperature after the cold surge occurrence, providing more moisture available for precipitation in East Asia and East North America, respectively. Overall, the results of the numerical experiments provide evidence that Antarctic sea‐ice loss influences cold surges in Northern Hemisphere through atmospheric teleconnections. It is important to continue investigating the link between Antarctic sea‐ice loss and weather events like cold surges, as this research can help improve our understanding of the impacts of polar climate change on lower latitudes. [ABSTRACT FROM AUTHOR]

In a changing climate, drought risk and vulnerability assessments are becoming increasingly important. Following the global call for proactive drought risk management, drought vulnerability assessments are progressively taking their stage in the drought research community. As the manifestation of drought vulnerability is dependent on the social, ecological, and hydroclimatic context in which it occurs, identifying vulnerability factors relevant for specific climatological and ecological regions may improve the quality of vulnerability assessments. Meanwhile, a holistic overview of factors affecting vulnerability in polar and cold climates is currently lacking. These regions are home to large socio-hydrological systems including urban areas, energy systems, agricultural practices, and the boreal forest. By conducting an interdisciplinary systematic literature review, the manifestation and conceptualization of drought vulnerability were identified for forested ecoregions in the Köppen– Geiger D and E climates. Vulnerability factors, as described by several scientific disciplines, were identified and combined into a conceptual framework for drought vulnerability in the study region. The results demonstrate the wide range of conceptualizations that exist for assessing drought vulnerability, and the thematic differences between sectors such as forestry, water supply, and agriculture. The conceptual framework presented herein adopts a novel approach, categorizing vulnerability factors by their location in a socio-hydrological system, and their relation to blue or green water sources. This allowed for identification of systemic vulnerability patterns, providing new insights into regional differences in drought vulnerability and a base for stakeholders performing proactive drought risk assessments in the study region. This article is categorized under: Human Water > Methods Science of Water > Water Extremes Water and Life > Conservation, Management, and Awareness Human Water > Water Governance [ABSTRACT FROM AUTHOR]

Ocean heat exchanges at the marginal ice zone (MIZ) play an important role in melting sea ice. Mixed‐layer eddies transport heat and ice floes across the MIZ, facilitating the pack's access to warm waters. This study explores these frontal dynamics using disk‐shaped floes coupled to an upper‐ocean model simulating the sea ice edge. Numerical experiments reveal that small floes respond more strongly to fine‐scale ocean currents, which favors higher dispersion rates and weakens sea ice drag onto the underlying ocean. Floes with radii smaller than resolved turbulent filaments (∼2–4 km) result in a wider and more energetic MIZ, by a factor of 70% each, compared to larger floes. We hypothesize that this floe size dependency may affect sea ice break‐up by controlling oceanic energy propagation into the MIZ and modulate the sea ice pack's melt rate by regulating lateral heat transport toward the sea ice cover. Plain Language Summary: Sea ice forms as a thin layer of frozen ocean waters, which breaks into individual floes due to the action of waves, ocean currents, and atmospheric winds. At the edge of the pack, these floes are vulnerable to warm waters in the open ocean, which can favor the melt of sea ice. The transport of heat from the open ocean into ice‐covered regions is not well represented in existing climate models, notably due to their poor spatial resolution and their inability to represent the dynamics of individual floes. In this study, we use a regional numerical model to investigate how fine‐scale ocean currents (2–30 km) can help transport heat toward a sea ice pack composed of broken‐up floes. We find that this heat transport is most efficient when floes are small, because they cannot efficiently damp the mechanical energy from the surface currents and they are easily transported into the open ocean by these currents. These two processes combined may lead to sea ice melt feedbacks that are currently not captured by coarser climate models. Key Points: The sensitivity of sea ice dispersion and upper‐ocean energetics to floe size is considered at a mesoscale frontFloes smaller than turbulent filaments disperse more strongly and lead to a wider marginal ice zoneThese small floes allow for stronger eddy kinetic energy propagation and heat transport into the pack [ABSTRACT FROM AUTHOR]

A new, simple parameterization scheme for scalar (heat and moisture) exchange over sea ice and the marginal ice zone is tested in a numerical weather and climate prediction model. This new "Blended A87" scheme accounts for the influence of aerodynamic roughness on the relationship between momentum and scalar exchange over consolidated sea ice, in line with long‐standing theory and recent field observations, and in contrast to the crude schemes currently operational in most models. Using aircraft observations and Met Office Unified Model simulations of cold‐air outbreak (CAO) conditions over aerodynamically rough sea ice, we demonstrate striking improvements in model performance when the Blended A87 scheme replaces the model's operational treatment for surface scalar exchange, provided that the aerodynamic roughness over consolidated ice is appropriately prescribed. The mean biases in surface sensible heat flux, surface latent heat flux, near‐surface air temperature, and surface temperature reduce from 25 to 11 W m−2, 22 to 12 W m−2, 0.8 to 0.0 K, and 1.4 to 0.8 K, respectively. We demonstrate that such impacts on surface exchange over sea ice can have a marked impact on the evolution of the atmospheric boundary layer across hundreds of kilometres downwind of the sea ice during CAO conditions in the model. Our results highlight the importance of spatiotemporal variability in the topography of consolidated sea ice for both momentum and scalar exchange over sea ice; accounting for which remains a key challenge for modeling polar weather and climate. Plain Language Summary: A new algorithm for the turbulent exchange of heat and moisture between the atmosphere and the ice‐covered oceans of the polar regions is tested in a state‐of‐the‐art weather and climate model. The algorithm is applicable both over consolidated sea ice and in regions characterized by a mixture of open seawater and ice. It accounts for the influence of aerodynamic roughness (a function of wind speed and the fine‐scale topographic roughness of the surface), in line with long‐standing theory and recent field observations, and in contrast to the crude schemes currently operational in most models. Using low‐altitude aircraft observations from over the Arctic Ocean and Nordic Seas, we demonstrate striking improvements in model performance when the new algorithm replaces the model's operational treatment for surface scalar exchange, provided that the aerodynamic roughness over consolidated ice is appropriately prescribed. The mean biases in surface sensible heat flux, surface latent heat flux, near‐surface air temperature and surface temperature reduce from 25 to 11 W m−2, 22 to 12 W m−2, 0.8 to 0.0 K, and 1.4 to 0.8 K, respectively. We demonstrate that such impacts on surface exchange over sea ice can have a significant impact on model prediction of high‐latitude weather. Key Points: The model reproduction of scalar fluxes over sea ice is improved with a new parameterization that accounts for aerodynamic roughnessThe properties and structure of the polar atmospheric boundary layer are sensitive to the implementation of this new parameterizationThe benefit of the parameterization accounting for aerodynamic roughness hinges on the appropriate prescription of sea‐ice topography [ABSTRACT FROM AUTHOR]

Glacier and ice sheet surfaces host diverse communities of microorganisms whose activity (or inactivity) influences biogeochemical cycles and ice melting. Supraglacial microbes endure various environmental extremes including resource scarcity, frequent temperature fluctuations above and below the freezing point of water, and high UV irradiance during summer followed by months of total darkness during winter. One strategy that enables microbial life to persist through environmental extremes is dormancy, which despite being prevalent among microbial communities in natural settings, has not been directly measured and quantified in glacier surface ecosystems. Here, we use a combination of metabarcoding and metatranscriptomic analyses, as well as cell‐specific activity (BONCAT) incubations to assess the diversity and activity of microbial communities from glacial surfaces in Iceland and Greenland. We also present a new ecological model for glacier microorganisms and simulate physiological state‐changes in the glacial microbial community under idealized (i) freezing, (ii) thawing, and (iii) freeze–thaw conditions. We show that a high proportion (>50%) of bacterial cells are translationally active in‐situ on snow and ice surfaces, with Actinomycetota, Pseudomonadota, and Planctomycetota dominating the total and active community compositions, and that glacier microorganisms, even when frozen, could resume translational activity within 24 h after thawing. Our data suggest that glacial microorganisms respond rapidly to dynamic and changing conditions typical of their natural environment. We deduce that the biology and biogeochemistry of glacier surfaces are shaped by processes occurring over short (i.e., daily) timescales, and thus are susceptible to change following the expected alterations to the melt‐regime of glaciers driven by climate change. A better understanding of the activity of microorganisms on glacier surfaces is critical in addressing the growing concern of climate change in Polar regions, as well as for their use as analogues to life in potentially habitable icy worlds. [ABSTRACT FROM AUTHOR]

Water storage capacity in the layers of canopy, litter, and soil of forest ecosystems has not yet been thoroughly investigated on a global scale. We estimated the global pattern of water storage capacity of forest ecosystems related to water regulation services (WSCFE) in the above three layers based on 1,288 observations and analyzed their 22 controlling environmental factors. The results show that the global mean WSCFE per unit area is 456.7 mm, and the total volume of WSCFE is 22,662.5 km3. Climatic variables are the leading factors contributing to the variations of WSCFE, followed by forest attributes, terrain factors, soil properties, and litter characteristics. This study advances the understanding of the large‐scale variation mechanisms of WSCFE in different forest types and climate zones and provides scientific evidence for ecological protection according to local conditions. Plain Language Summary: Forest ecosystem plays a vital role in the earth's hydrological process, and water storage capacity of forest ecosystems related to water regulation service (WSCFE) is of vital importance for human well‐being. Water can be intercepted by forest canopy, be held by litter, and be stored in soils, which accounts for more than a quarter of the water volumes in the terrestrial hydrologic cycle. The WSCFE is affected by many factors and its global pattern has not been well understood. In this study, based on the observed data from literature, we provided a robust global pattern of the WSCFE in canopy layer, litter layer, and soil layer. The results show that the WSCFE in the canopy and soil layer decrease gradually from tropical climate zone to polar climate zone, while the maximum WSCFE in the litter layer appears in polar and cold climate zone. The main controlling factors have different impacts on the WSCFE in the three layers. These should be considered in the developing protection policies for important ecological functional areas. Key Points: Forest water storage capacity related to water regulation decreases from equator to pole, from coast to inland, and from mountains to plainsAmong the controlling factors, climatic factors have the largest and most positive influence on water storage capacityThe quantification of three important water storages provides a basis to delineate global water regulation zones [ABSTRACT FROM AUTHOR]

Much of the salty, high oxygen North Atlantic Deep Water (NADW) leaving the Atlantic flows through the Argentine Basin, where it is diluted by fresher, low oxygen Circumpolar Deep Water (CDW). This mixing of deep water masses is often overlooked in the zonally averaged description of the overturning circulation. Here, we show that intense mixing occurs along the western boundary: (a) extreme, isolated oxygen/temperature anomalies recorded by three autonomous biogeochemical floats suggest that subsurface eddies can inject relatively unmodified CDW far into the northwestern Argentine Basin, and (b) moderate, numerous temperature/salinity anomalies indicate a mixing zone from Rio Grande Rise to the Malvinas Current. This western eddy pathway shortcuts the gyre‐scale cyclonic route for CDW inferred from most previous studies. Significantly, CDW dilution of NADW affects the properties of deep waters that upwell in the Southern Ocean, and hence the connection between Northern and Southern Hemisphere polar climates. Plain Language Summary: Water, heat, and carbon are transported around the global ocean by the meridional overturning circulation, which helps regulate the climate system. In the Atlantic Ocean, the overturning circulation is characterized by net southward flow in the deep water layers, which transports water from the northern North Atlantic (North Atlantic Deep Water; NADW) all the way to the Southern Ocean. Often neglected in this picture is the modification of these deep waters as they flow south toward the Antarctic. Specifically, they become colder, fresher and less oxygenated due to mixing with much older deep water from the South Pacific, which enters the Atlantic below South America and joins the Circumpolar Deep Water (CDW) flowing northward into the Argentine Basin. Here, using autonomous float measurements, we investigate the mixing between NADW and CDW in the Argentine Basin. We show that isolated boluses of CDW with properties from the Malvinas are found far to the north on the western side of the basin, suggesting transport by isolated subsurface eddies. Understanding these pathways is important because they influence the properties of the water that rises to the surface in the Southern Ocean; dilution of NADW by CDW damps the transmission of Northern Hemisphere climate change to the Southern Ocean. Key Points: Pacific/Circumpolar Deep Water (CDW) with low oxygen, salinity, and pH dilutes North Atlantic Deep Water (NADW) in the South Atlantic's Argentine BasinIsolated low oxygen anomalies in the northwest Argentine Basin indicate a direct path of CDW northward via the MalvinasStrong isopycnic temperature variability along the western boundary identifies this as a mixing hotspot for these two deep water masses [ABSTRACT FROM AUTHOR]

For this reason, climate refugia and climate-informed ecosystem-based management are both vital to maximize the resilience of species and ecosystem processes in these cold, polar habitats (Chown et al., 2022; Constable, 2022). In the Arctic terrestrial sphere, warming, permafrost thaw and snowfall decrease have led to profound landscape, ecosystem structure and hydrological changes (Fujii et al., 2022). Polar landscapes and their unique biodiversity are threatened by climate change. [Extracted from the article]

Satellite sea-ice thickness observations are shown to be key to improving seasonal predictions of summer Arctic sea-ice concentration. The decrease in high-latitude surface albedo caused by the vanishing Arctic sea ice has a distinct signature on the Earth's radiative balance (Pistone I et al i ., [6]). The study shows that I in situ i observations play a critical role in initializing numerical weather forecasts during the winter season, while satellite microwave sounders are crucial during the summer season. [Extracted from the article]

Using four reanalysis data sets and ground‐based observations, this paper uncovers that on average, 30% of the time, Northern Hemisphere snow cover experiences unfrozen bottom soil. It is demonstrated that the probability of occurrence of unfrozen soils is correlated with the snow types and is maximum over the ephemeral followed by the maritime and prairie snow. The results based on reanalysis data unveil that the seasonal evolution of the unfrozen soil areas is not synchronous with the snow cover extent and exhibits sub‐annual bi‐modality with two annual maxima in April and October. Interannual trend analyses indicate that shrinkage of spring snow in the past few decades has been accompanied by an increase in the proportion of unfrozen bottom soils, more significantly over polar climate regimes dominated by the tundra and taiga snow. The findings imply that the snowpack basal melting could have increased due to global warming. Plain Language Summary: Unfrozen bottom soils below snow layers play an important role in the persistence and stability of snowpack, yet less knowledge is known about its spatial variability and seasonal evolution on a global scale. This study uncovers that, on average, around 30% of annual Northern Hemisphere's snow cover extent is over unfrozen soils with a spatial variability that is highly correlated with snow types. Specifically, unfrozen soils appear more frequently below the ephemeral followed by the maritime and prairie snow. In addition, it is demonstrated that the unfrozen soil areas exhibit different seasonal evolution from snow cover extent with two annual peaks in April and October. The results show that the areas of unfrozen soils are expanding in spring as the snow cover extent is shrinking. Key Points: On average 30% of the year the soil below global snowpack is unfrozenSeasonal evolution of the areas of unfrozen soil below snowpack is not synchronous with snow cover extentBasal snowpack melting could have increased in a warming climate [ABSTRACT FROM AUTHOR]

Summary: Snow algae are predicted to expand in polar regions due to climate warming, which can accelerate snowmelt by reducing albedo. Green snow frequently occurs near penguin colonies, and red snow distributes widely along ocean shores. However, the mechanisms underpinning the assemblage of algae and heterotrophs in colored snow remain poorly characterized.We investigated algal, bacterial, and fungal communities and their interactions in red and green snows in the Antarctic Peninsula using a high‐throughput sequencing method.We found distinct algal community structure in red and green snows, and the relative abundance of dominant taxa varied, potentially due to nutrient status differences. Contrastingly, red and green snows exhibited similar heterotrophic communities (bacteria and fungi), whereas the relative abundance of fungal pathogens was substantially higher in red snow by 3.8‐fold. Red snow exhibited a higher network complexity, indicated by a higher number of nodes and edges. Red snow exhibited a higher proportion of negative correlations among heterotrophs (62.2% vs 3.4%) and stronger network stability, suggesting the red‐snow network is more resistant to external disturbance.Our study revealed that the red snow microbiome exhibits a more stable microbial network than the green snow microbiome. [ABSTRACT FROM AUTHOR]

The uncertainty in polar cloud feedbacks calls for process understanding of the cloud response to climate warming. As an initial step toward improved process understanding, we investigate the seasonal cycle of polar clouds in the current climate by adopting a novel modeling framework using large eddy simulations (LES), which explicitly resolve cloud dynamics. Resolved horizontal and vertical advection of heat and moisture from an idealized general circulation model (GCM) are prescribed as forcing in the LES. The LES are also forced with prescribed sea ice thickness, but surface temperature, atmospheric temperature, and moisture evolve freely without nudging. A semigray radiative transfer scheme without water vapor and cloud feedbacks allows the GCM and LES to achieve closed energy budgets more easily than would be possible with more complex schemes. This enables the mean states in the two models to be consistently compared, without the added complications from interaction with more comprehensive radiation. We show that the LES closely follow the GCM seasonal cycle, and the seasonal cycle of low‐level clouds in the LES resembles observations: maximum cloud liquid occurs in late summer and early autumn, and winter clouds are dominated by ice in the upper troposphere. Large‐scale advection of moisture provides the main source of water vapor for the liquid‐containing clouds in summer, while a temperature advection peak in winter makes the atmosphere relatively dry and reduces cloud condensate. The framework we develop and employ can be used broadly for studying cloud processes and the response of polar clouds to climate warming. Plain Language Summary: The polar regions are changing rapidly. Clouds and their feedbacks remain uncertain due to small‐scale unresolved processes in climate models, which contribute to uncertainties in polar climate projection. In order to understand the mechanisms that control polar clouds, we focus on their seasonal cycle in the current climate. We adopt an idealized framework for driving high‐resolution simulations by a global climate model. With minimal components represented, we find similar features between the simulated and observed polar clouds. In particular, liquid‐containing clouds reach maximum in summer, which coincides with the summer peak in moisture advection from lower latitudes. Therefore, projection of polar clouds will depend on future changes in heat and moisture advection. This framework will allow us to study the response of polar clouds to climate warming. Key Points: Large eddy simulations driven by time‐varying large‐scale forcings from an idealized general circulation model is used to simulate the seasonal cycle of Arctic cloudsSimulated low‐level cloud liquid is maximal in late summer to early autumn, and minimal in winter, consistent with observationsLarge‐scale advection provides the main moisture source for cloud liquid and shapes its seasonal cycle [ABSTRACT FROM AUTHOR]

Significant progress has been made in our understanding of extratropical impacts on the tropical climate via energetics framework. It is of question whether the impact of extratropical thermal forcing in one hemisphere would extend far into high‐latitudes of the other hemisphere. We examine the possibility of the pole‐to‐pole linkage via atmospheric teleconnections by imposing a cyclic surface thermal forcing in the northern extratropics of an aquaplanet slab ocean model. We reveal a synchronous temperature response between the two poles mediated by zonal‐mean atmospheric dynamics. A warming in one polar region leads to a strengthened Hadley circulation of the unforced hemisphere, fluxing more momentum toward the subtropics, thereby pulling the eddy‐driven jet equatorward. A consequent anomalous descent over the polar region causes warming. The polar surface warming in the unforced hemisphere reaches 30% of that in the forced hemisphere, inferring a significance of the pole‐to‐pole connection. Plain Language Summary: Regional climate change effects can be global. This paper reveals a pole‐to‐pole linkage in the absence of ocean dynamics. A high‐latitude surface thermal forcing confined to one hemisphere causes changes in the tropical circulation and mid‐latitude jet, thereby inducing a secondary circulation in the unforced hemisphere. The atmosphere‐driven pole‐to‐pole connection is characterized by synchronous temperature changes between the two poles. We speculate the factors not considered in this study such as ocean‐biogeochemistry feedback may shift temperature changes from being synchronous to asynchronous on longer than multidecadal timescales. Hence, future studies are warranted that gradually add complexities to a model to elaborate pole‐to‐pole teleconnection. Key Points: High‐latitude thermal forcing confined to one hemisphere can cause surface temperature changes globally including the opposite poleThe pole‐to‐pole linkage via atmospheric pathway results in synchronous polar temperature changesThe interhemispheric teleconnection leads to mini‐global warming in response to heating confined to one hemisphere [ABSTRACT FROM AUTHOR]

Greenland ice sheet rainfall is expected to increase under a warming climate. Yet, there have been no active long‐term in‐situ rainfall records on the ice sheet due to observational difficulties. Here, we utilize the state‐of‐the‐art 5 km polar non‐hydrostatic regional climate model NHM‐SMAP to evaluate the ice sheet's rainfall over 40 years (1980–2019). The largest trends include a fourfold increase in annual rainfall for the northwestern ice sheet; 3.1 Gt year−1 or 12 mm m−2 year−1. September ice‐sheet‐wide rainfall amount and intensity increase by 7.5 Gt month−1 and 20.8 mm h−1 year−1. In the last two decades, the increasing September maximum hourly rainfall rate exceeded 50 mm h−1 six times. The increased surface water delivery has numerous implications, including for snow metamorphism and ice flow dynamics. Plain Language Summary: We find that rainfall has increased over the Greenland ice sheet from 1980 to 2019. Among the eight major ice‐sheet drainage areas, the northwestern sector stands out as an increasing rainfall hotspot where the annual rainfall has increased fourfold. For the entire ice sheet, September's total rainfall and its intensity increased by 224% and 54% above the 1981–2010 baseline over the last 40 years. An increase in late melt season rainfall is expected to contribute to an increase in late summer snow and ice melt. Our results provide the first detailed quantification of the state of ice sheet rainfall climatology. Key Points: A 5 km horizontal resolution non‐hydrostatic regional climate model is used to evaluate Greenland ice sheet rainfall from 1980 to 2019The northwestern sector stands out as a hotspot of increasing rainfallBoth the amount and intensity of September ice‐sheet‐wide rainfall have significantly increased in the 40 years from 1980 to 2019 [ABSTRACT FROM AUTHOR]

It is challenging to estimate how the regional climate will be shifted under future global warming. To reduce the potential risk of regional climate shift under future climates, examining the change in climate features over Asia is important, as approximately 60% of the world's population resides there. In this study, climate shifts are assessed over the Asian monsoon region under global mean temperature warming targets from 1.5°C to 5.0°C above preindustrial (PI) levels based on different shared socioeconomic pathway (SSP) scenarios. Global warming impacts the individual climate variables, and consequently, it impacts the regional climate features across the Asian region. Temperature change patterns are more dominant contributors to the spatial extent and magnitude of climate shifts than precipitation change patterns. Changes in regional climates show different behaviors according to the degree of global warming rather than the type of SSP scenario. Climate shifts are intensified under a higher level of global warming that is above the PI levels. The largest climate shifts in this region are shown under global warming of 5.0°C based on the SSP5‐8.5 scenario, especially in current polar climate zones. Future change patterns in individual climate zone can differ. Regions with tropical climates and arid climates are likely to be expanded, whereas some regions with warm temperate climates, cold climates, and polar climates are likely to shrink under global warming conditions. Therefore, this study supports the necessity of mitigating greenhouse gas (GHG) emissions and establishing an adaptation plan for future global warming conditions. Key Points: Potential global warming based on CMIP6 causes the significant changes in regional climates and consequently climate shifts over AsiaPace of climate zone shifts will become faster as the global warms, but the differences exist among the regional climate featuresCharacteristics of climate shifts are more sensitive to the degree of global mean temperature increase than the type of SSP scenarios [ABSTRACT FROM AUTHOR]

This paper presents a multivariate classification of the global wave climate into types driven by atmospheric circulation patterns. The primary source of the net long-term variability is evaluated based on historical wave simulations. Results show that the monsoon, extratropical, subtropical, and polar wave climate types of the Pacific and North Atlantic Oceans are dominated by natural variability, whereas the extratropical and subtropical wave climate types in the Indian Ocean, and the tropical wave climate types of the Atlantic and Pacific Oceans exhibit a global warming signal. In the Pacific sector of the Southern Ocean, strong natural variability may mask a global warming signal that is yet to emerge as being statistically significant. In addition, wave climate teleconnections were found across the world that can provide a framework for joint strategies to achieve the goals of climate adaption for resilient coastal communities and environments. Plain Language Summary Near-surface wind systems drive global ocean wave conditions that are usually studied at regional or local scale. However, analyzing these relationships at the global scale is important to understand how natural climate oscillations, such as El Niño-Southern Oscillation, and global warming, impact wave climate. Here we identify the large wave climates in homology to the climate regions (e.g., Tropical, Temperate, Polar) and are originated by the planetary wind systems. The results show that global warming signals have already emerged in the Indian Ocean and the tropical regions of the Pacific and Atlantic basins. In contrast, in the other ocean basins, natural variability is still the dominant signal and could mask global warming signals. [ABSTRACT FROM AUTHOR]

Secular polar drift underwent a directional change in the 1990s, but the underlying mechanism remains unclear. In this study, polar motion observations are compared with geophysical excitations from the atmosphere, oceans, solid Earth, and terrestrial water storage (TWS) during the period of 1981–2020 to determine major drivers. When contributions from the atmosphere, oceans, and solid Earth are removed, the residual dominates the change in the 1990s. The contribution of TWS to the residual is quantified by comparing the hydrological excitations from modeled TWS changes in two different scenarios. One scenario assumes that the TWS change is stationary over the entire study period, and another scenario corrects the stationary result with actual glacier mass change. The accelerated ice melting over major glacial areas drives the polar drift toward 26°E for 3.28 mas/yr after the 1990s. The findings offer a clue for studying past climate‐driven polar motion. Plain Language Summary: The Earth's pole, the point where the Earth's rotational axis intersects its crust in the Northern Hemisphere, drifted in a new eastward direction in the 1990s, as observed by space geodetic observations. Generally, polar motion is caused by changes in the hydrosphere, atmosphere, oceans, or solid Earth. However, short‐term observational records of key information in the hydrosphere (i.e., changes in terrestrial water storage) limit a better understanding of new polar drift in the 1990s. This study introduces a novel approach to quantify the contribution from changes in terrestrial water storage by comparing its drift path under two different scenarios. One scenario assumes that the terrestrial water storage change throughout the entire study period (1981–2020) is similar to that observed recently (2002–2020). The second scenario assumes that it changed from observed glacier ice melting. Only the latter scenario, along with the atmosphere, oceans, and solid Earth, agrees with the polar motion during the period of 1981–2020. The accelerated terrestrial water storage decline resulting from glacial ice melting is thus the main driver of the rapid polar drift toward the east after the 1990s. This new finding indicates that a close relationship existed between polar motion and climate change in the past. Key Points: Past climate‐driven polar motion was quantified by modeling terrestrial water storage under two different scenariosOne scenario was based on GRACE and reanalysis data; another scenario was based on extra glacier change observationsRapid terrestrial water storage decline caused by ice melting over glacial areas drove the polar drift toward the east in the 1990s [ABSTRACT FROM AUTHOR]

Using both observation and CMIP5 simulation data, this study investigates the shifts of climate zones from a landscape perspective on the Arctic for the period 1940–2013. The results reveal that the reduction in area is often accompanied by the fragmentation of the spatial structure. In terms of percentage of landscape, the coverage of polar climate zone had undergone a rapid decrease from 1940 to 2013. Moreover, the polar climate has been facing an intensified fragmentation over the time 1940–2013. Further analysis shows that this fragmentation phenomenon can be attributed more to anthropogenic than natural forcing from 1940 to 2003, even though the change in patch density is not steady, by comparison of observations and simulation results. In addition, the fragmentation in the Arctic climate zone depends on the horizontal resolution of data. Although the fragmentation trends of observations at three spatial resolutions of 2°–0.5° are consistent, the magnitude of trends weakens as the spatial resolution decreases. [ABSTRACT FROM AUTHOR]

Most climate models neglect cloud longwave (LW) scattering because scattering is considered negligible compared to strong LW absorption by clouds and greenhouse gases. While this rationale is valid for simulating extrapolar regions, it is questionable for the polar regions, where the atmosphere is dry and hence has weak absorption, and ice clouds that have strong scattering capability frequently occur. Using the slab‐ocean Community Earth System Model, we show that ice cloud LW scattering can warm winter surface air temperature by 0.8–1.8 K in the Arctic and 1.3–1.9 K in the Antarctic, while this warming becomes much weaker in polar summer. Such scattering effect cannot be correctly assessed when sea surface temperature and sea ice are prescribed as this effect is manifested through a surface‐atmosphere coupling. Cloud LW scattering is a necessity for the correct simulation of polar climate and surface radiation budget, especially in the winter. Plain Language Summary: Cloud longwave scattering has never been deemed as a necessity in climate models. Out of all climate models in the IPCC fifth and sixth assessments, only three modeling centers have longwave scattering included in their models. Our study explained why the traditional wisdom of neglecting longwave scattering breaks down for the simulation of high‐latitude climate in the fully coupled models. We showed the critical importance of atmosphere‐surface radiative coupling for correctly assessing the role of cloud longwave scattering in the model simulation of climate mean state as well as climate changes, an issue overlooked by all previous studies. We argued that the cloud longwave scattering is a necessity in climate models, not an option. Key Points: Cloud longwave scattering is more important in the polar regions than the extrapolar regionsBy surface‐atmosphere radiative coupling, cloud longwave scattering can warm the polar surface, more in the winter than in the summerCloud longwave scattering is a necessity instead of an option for correctly simulating polar climate and surface energy budget [ABSTRACT FROM AUTHOR]

Climate and environmental condition drive biodiversity at many levels of biological organization, from populations to ecosystems. Combined with paleoecological reconstructions, palaeogenetic information on resident populations provides novel insights into evolutionary trajectories and genetic diversity driven by environmental variability. While temporal observations of changing genetic structure are often made of sexual populations, little is known about how environmental change affects the long‐term fate of asexual lineages. Here, we provide information on obligately asexual, triploid Daphnia populations from three Arctic lakes in West Greenland through the past 200–300 years to test the impact of environmental change on the temporal and spatial population genetic structure. The contrasting ecological state of the lakes, specifically regarding salinity and habitat structure may explain the observed lake‐specific clonal composition over time. Palaeolimnological reconstructions show considerable regional environmental fluctuations since 1,700 (the end of the Little Ice Age), but the population genetic structure in two lakes was almost unchanged with at most two clones per time period. Their local populations were strongly dominated by a single clone that has persisted for 250–300 years. We discuss possible explanations for the apparent population genetic stability: (a) persistent clones are general‐purpose genotypes that thrive under broad environmental conditions, (b) clonal lineages evolved subtle genotypic differences unresolved by microsatellite markers, or (c) epigenetic modifications allow for clonal adaptation to changing environmental conditions. Our results motivate research into the mechanisms of adaptation in these populations, as well as their evolutionary fate in the light of accelerating climate change in the polar regions. [ABSTRACT FROM AUTHOR]

A novel decomposition of the ocean heat energy that contributes to sea ice melt and growth (ocean‐ice and frazil heat) into components that are driven by surface heat flux and ocean circulation changes is used to isolate the evolving roles of the atmosphere and ocean in the Arctic sea ice loss from CO2 increases. A sea ice volume budget analysis is used to separate the impacts of the anomalous frazil/ocean‐ice heat from those of atmosphere‐ice heat on the evolving Arctic sea ice volume. The role of atmosphere‐ocean coupling in augmenting or curtailing the atmosphere‐ and ocean‐driven sea ice losses is further isolated by comparing the ice volume budget and the anomalous frazil/ocean‐ice heat components in partially and fully coupled experiments. Atmosphere‐ice heat fluxes drive most of Arctic sea ice loss in the first decade following CO2 increase by increasing the sea ice top face melt in summer, while ocean circulation changes drive the loss over the longer term through the anomalous increase of heat transport into the Arctic, which drive decreases in frazil ice growth and sea ice extent in winter. Atmosphere‐ocean coupling in the subpolar Atlantic further supports a negative feedback that attenuates the ocean‐driven sea ice losses over time; by accelerating the weakening of the Atlantic meridional overturning circulation, it causes a large cooling of the subpolar Atlantic and attenuation of the anomalous heat transport into the Arctic in winter, allowing for a seasonal Arctic sea ice in the fully coupled experiment, while the Arctic completely becomes ice free in the partially coupled experiment. Plain Language Summary: The interactions between the atmosphere, ocean, and sea ice are disentangled in order to isolate their individual roles in driving Arctic sea ice losses and how these roles change over time. We introduce a new decomposition of the ocean heat that contributes to melting and growing sea ice into parts that are caused by changes in the surface heat input into the ocean and ocean circulation. We analyze the contributions of the ocean heat and atmosphere heat to the overall Arctic sea ice volume changes, both in an experiment where a two‐way interaction between the atmosphere and ocean is allowed and in another where this two‐way interaction is not allowed. Our results suggest that the atmosphere causes most of Arctic sea ice loss (within a decade) by increasing sea ice top face melt, while the ocean causes the long‐term sea ice changes in the Arctic by decreasing winter bottom face growth. The interactions between the atmosphere and ocean further enhance the ocean circulation weakening and surface cooling in the subpolar Atlantic and thereby stop the winter heat transport increase into the Arctic and eventually curtail the ocean‐driven sea ice loss and prevent the total loss of Arctic sea ice. Key Points: A novel decomposition isolates how ocean surface heating, circulation changes, and air‐sea interactions drive sea ice loss from CO2 increasesAtmosphere changes determine Arctic sea ice loss within the first decade; ocean circulation changes drive longer term ice lossesAtmosphere‐ocean coupling feedbacks on ocean circulation change in the subpolar Atlantic stabilizes Arctic sea ice loss in the long term [ABSTRACT FROM AUTHOR]

In order to understand the pure long‐term influence of single mega volcanic eruption (SMVE) of universal significance on global and polar region temperature changes, the AD 1258 Samalas mega volcanic eruption in Indonesia which is the largest eruption over the past millennium is selected as an ideal eruption for simulation study based on Community Earth System Model. Both reconstructions and simulations show that the Northern Hemisphere experienced nearly two decades of strong cooling after the Samalas mega eruption. The significant cooling in the Arctic lasts for 16 years, while the cooling in the Antarctic lasts only 2 years. As the volcanic aerosol gradually disappears, stronger cooling occurs in Arctic winter, and warming occurs in Antarctic winter. This asymmetric temperature changes over Arctic and Antarctic after SMVE (such as Samalas) are caused by the combined effects of albedo feedback and ocean‐atmosphere heat exchange related to sea ice. Plain Language Summary: Polar climate is the focus of earth system investigation because they are very sensitive to external forcings and its related impacts on global climate. Volcanic eruption is one of the important external factors affecting global and polar climate change. The AD 1258 Samalas mega volcanic eruption in Indonesia was the largest eruption over the past millennium, which makes it an ideal eruption to study pure long‐term climatic effects of single mega volcanic eruption (SMVE). Here, we use an Earth System Model and find that the duration of surface cooling caused by SMVE (such as Samalas) is longer than we generally believed before and varies in latitude. The Northern Hemisphere experienced nearly two decades of strong cooling after the Samalas event. The significant cooling in the Arctic lasts for 16 years, while the cooling in the Antarctic lasts only 2 years. The SMVE (such as Samalas) could expand Arctic sea ice for more than two decades, but the expansion of Antarctic sea ice lasts only 2–3 years. The asymmetric temperature changes over polar regions are influenced by the combined effects of albedo feedback and ocean‐atmosphere heat exchange related to sea ice. The knowledge gained from this research is critical for improved understanding of the potential long‐term impacts of SMVE on the projected future global and polar region temperature change. Key Points: Both reconstructions and simulations show that the NH experienced nearly two decades of strong cooling after the Samalas mega eruptionA single mega volcanic eruption will cause remarkable asymmetry of temperature variation and duration between the Arctic and AntarcticAsymmetric temperature changes are caused by the combined effects of albedo feedback and ocean‐atmosphere heat exchange related to sea ice [ABSTRACT FROM AUTHOR]

The variation of polar sea ice is an indicator of polar environmental change, which plays an important role in the study of regional and global climate change. In this paper, the latest sea ice data sets from the European Space Agency Climate Change Initiative were firstly combined to comprehensively analyze the spatial and temporal variation of Arctic sea ice concentration (SIC) and sea ice thickness (SIT) from 2002 to 2017. The results show that during this period, the SIC of the Kara Sea and the Barents Sea decreases the most significantly, reaching −1.11%·year−1. The Arctic annual average sea ice extent (SIE) and sea ice area (SIA) exhibit noticeable decreasing trends, reaching −0.0592 × 106 km·year−1 and −0.0628 × 106 km·year−1, respectively. Both of Arctic SIE and SIA vary seasonally, and they reach the minimum values of 4.97 × 106 km2 and 3.96 × 106 km2 in September and the maximum values of 14.58 × 106 km2 and 13.35 × 106 km2 in March, respectively. Moreover, the Arctic SIE and SIA anomaly series from 2002 to 2017 were analyzed based on the linear regression method. It is found the most noticeable decreasing trends of the Arctic SIE and SIA are from July to October. The maximum variation of the SIE is −1.06 × 106 km2(10a)−1, and the maximum variation of the SIA is −1.09 × 106 km2(10a)−1. The Arctic SIE and SIA present the smallest decreasing trends from April to May, which are −0.19 × 106 km2(10a)−1 and −0.2 × 106 km2(10a)−1, respectively. The Arctic SIT also displays a pronounced decreasing trend with −0.015 m·year−1 in autumn and −0.018 m·year−1 in winter. The annual average SIT reaches a minimum of 1.28 m in 2013 and a maximum of 1.66 m in 2005. Particularly, the SIT of the Hudson Bay decreases the most significantly, reaching −0.051 m·year−1. Finally, the Arctic average SIT was tested by the Mann‐Kendall method. It is found that the SIT has a sudden change in 2007, from a slight increase in 2003–2007 to a significant decrease in 2007–2017. Overall, the decreasing trend of the Arctic sea ice (both SIC and SIT) is significant in the past decade. These findings can contribute to future research on polar regions and global climate change. Key Points: We analyzed the whole and regional variation of Arctic sea ice by combining use of the latest sea ice concentration and sea ice thickness data sets from European Space AgencyThe sea ice concentration in the Barents Sea and the Kara Sea and the sea ice thickness in the Hudson Bay decreased the most obviouslyThe sea ice thickness has a sudden change in 2007 based on Mann‐Kendall mutation test [ABSTRACT FROM AUTHOR]

The global temperature has increased approximately 0.9°C over the past 50 years and is projected to continue to increase. Many efforts have been taken to investigate the evolutionary dynamics of climate classification zones in response to the rising temperature. However, the changing dynamics of the spatial climate patterns remain poorly understood. It is thus desired that the unobserved characteristics of the global climate patterns, such as aggregation and subdivision, are explored from the landscape perspective. Here, we demonstrate that the global climate zones have undergone a process of aggregation during the past 100 years and that this dynamic is expected to continue in the future. The climate aggregation effect is especially evident in the Arctic, Tibet, and East Africa. We find that the tropical, arid, temperate, and cold climates are aggregating while the polar climate zone exhibits subdivision. Furthermore, our analysis demonstrates a clear spatial aggregation process with a latitudinal feature. We should pay enough attention to the phenomenon of patch aggregation of global climate landscape pattern, which will undoubtedly help us to deepen our understanding of global climate change and help to further explore the feedback relationship between climate and biological systems. [ABSTRACT FROM AUTHOR]

Coupled ocean‐atmosphere models have been utilized to investigate the global climate response to polar sea ice loss using different approaches to constrain ice concentration and thickness. The goal of this study is to compare two commonly used methods within a single model framework: ice albedo reduction, which is energy conserving, and ice‐flux nudging, which is not energy conserving. The two approaches generate virtually identical equilibrium global climate responses to the same seasonal cycle of sea ice loss. However, while ice‐flux nudging is able to control the sea ice state year‐round, albedo reduction is most effective during summer and lessens the effects of climate change in winter due to the underestimation of sea ice loss. These evaluations have implications for the Polar Amplification Model Intercomparison Project (PAMIP), which proposes a set of coordinated coupled model experiments but without a defined protocol on how to constrain sea ice. Plain Language Summary: What does polar amplification mean for global climate? This question has been addressed by using different arbitrary methods to isolate melting of Arctic and/or Antarctic sea ice in coupled ocean‐atmosphere modeling experiments. However, these experiments sometimes obtained different answers. It is still unclear whether the divergent results arise from models' structural differences or from the different methods used to melt sea ice. In this study, two commonly used approaches (albedo reduction and nudging) are applied to a single climate model to generate the same seasonal cycle of ice loss and polar amplification. Nearly identical responses are found, including slowing down the thermohaline circulation in the Atlantic Ocean, weakened westerly winds over high latitudes, increased precipitation over the west coast of North America associated with a deepened Aleutian Low, and tropical upper tropospheric warming. However, ice albedo reduction is found to be ineffective in winter, unlike nudging, which can control sea ice year‐round. We therefore recommend nudging to be adopted for the Polar Amplification Model Intercomparison Project (PAMIP) coupled experiments. Key Points: Two ice‐constraining approaches in coupled models (albedo and nudging) to study the climate responses of future ice loss are evaluatedGiven the same seasonal cycle of ice loss, ice albedo reduction and ice‐flux nudging generate very similar global climate responsesIce albedo reduction underestimates projected winter sea ice loss and thus its impacts, with implications for coordinated model experiments [ABSTRACT FROM AUTHOR]

This study quantifies future changes in the polar cold air mass (PCAM) below a threshold potential temperature of 280 K and its horizontal fluxes, which are an indicator for the intensity of cold air outbreaks, by analyzing the outputs from five climate models from the Fifth Coupled Model Intercomparison Project. Under the business‐as‐usual scenario, the multimodel means of the wintertime total hemispheric PCAM decrease by 37% in the Northern Hemisphere and by 34% in the Southern Hemisphere by the end of the 21st century. The midlatitude equatorward PCAM fluxes are projected to decrease significantly by around 2050. This is primarily due to the reduction of the PCAM and to a lesser extent due to the weakening of the extratropical meridional circulation. Finally, intermodel differences in the total hemispheric PCAM reduction are shown to be linearly related to the climate sensitivity to the global mean surface air temperature. Plain Language Summary: In winter, the polar regions are reservoirs of extremely cold air masses. Sometimes, the polar cold air outflows to the midlatitudes and results in very cold weather. This study quantitatively evaluated the future changes in the polar cold air mass and its outflow to the midlatitudes in the winter hemispheres. We found that both the polar cold air mass and its outflow are projected to decrease significantly by the end of the 21st century in the Northern and Southern Hemispheres due to the increase in the global mean surface temperature. These findings provide a possible scenario of future polar climate change. Key Points: Under the RCP8.5 scenario, the polar cold air mass is projected to decrease by 37% in the boreal winter by the end of 21st centuryThe equatorward polar cold air mass fluxes in the midlatitudes are projected to decrease significantly by around 2050Thermodynamical (dynamical) change is the main (secondary) contributor to the projected reduction in the polar cold air mass fluxes [ABSTRACT FROM AUTHOR]

Arctic terns spend their breeding and non‐breeding seasons in polar environments at opposite ends of the world. The sensitivity of polar regions to climate change makes it essential to understand the ecology of arctic terns but the remoteness of the Antarctic presents a considerable challenge. One solution is to use 'biologgers' to monitor remotely their behaviour and distribution in the Antarctic. Data from birds tagged with light‐level global location sensors (geolocators) in 2015 and 2017 showed that a third of their annual cycle was spent amongst Antarctic sea ice. After reaching the East Antarctic in the austral spring, they gradually moved west, foraging in fragmented ice zones of the Antarctic coastline, leaving in the austral autumn for their return northward migration via the Atlantic. Changes in patterns of movement between phases of 24‐h daylight and diel day/night conditions were likely linked to the annual moult, and stable isotope analyses suggest that krill (Euphausia species) was an important component of their diet. There were marked differences in movement behaviour between arctic terns tagged in 2015 compared to 2017 that may relate to unusual changes in sea‐ice extent. The arctic tern may be unique amongst seabirds that utilise the Antarctic environment in summer in being able to move widely without nesting constraints, and may present a means of characterising the effects of climate change on species dependent for foraging on Antarctic sea‐ice and krill. [ABSTRACT FROM AUTHOR]

The South Polar Layered Deposits (SPLD) are the largest water ice reservoirs on Mars. Their accumulation is believed to result from climate oscillations that drive the movement of ice and dust on the surface. The High‐Resolution Imaging Science Experiment and the Colour and Stereo Surface Imaging System have imaged exposures of its internal structure in troughs and marginal scarps. Here we use the stereo imaging products of these instruments to extract stratigraphic profiles representative of various locations throughout the SPLD. Through wavelet and series‐matching analyses of these profiles, we reveal periodicities in the stratigraphy that correlate to the orbital oscillations that drive climate change on Mars and that have been observed to force the accumulation of the north polar cap. We infer that the water ice and dust of the SPLD were deposited at variable rates of 0.13–0.39 mm/year, taking a minimum of 10–30 Myr to accumulate. Plain Language Summary: The single location on Mars with the most water ice is in the southern polar ice cap, in the so‐called South Polar Layered Deposits (SPLD). Changes in Martian climate through time affect the locations on Mars where ice is stable, and it is believed that these changes drove the accumulation of layers upon layers of ice and dust in the SPLD. The High‐Resolution Imaging Science Experiment and the Colour and Stereo Surface Imaging System are satellite cameras that have photographed troughs and scarps within the SPLD to produce 3‐D views of this layered internal structure. We analyzed this structure and found patterns in the layering related to variations of Mars' orbit and spin axis. These variations drive climate change on Mars, so our analysis confirms the connection between the SPLD and Mars' astronomical parameters. From this relationship, we inferred that the ice and dust of the SPLD took at least 10–30 Myr to accumulate. Key Points: Patterns in the stratigraphy of Mars' south polar ice sheet are consistent with orbital climate forcingMars' south polar ice sheet accumulated nonuniformly at rates of 0.11–0.39 mm/yearSimilar orbital oscillations forced the accumulation of the northern and southern ice sheets [ABSTRACT FROM AUTHOR]

Abstract: Greenhouse gas (GHG) additions to Earth's atmosphere initially reduce global outgoing longwave radiation, thereby warming the planet. In select environments with temperature inversions, however, increased GHG concentrations can actually increase local outgoing longwave radiation. Negative top of atmosphere and effective radiative forcing (ERF) from this situation give the impression that local surface temperatures could cool in response to GHG increases. Here we consider an extreme scenario in which GHG concentrations are increased only within the warmest layers of winter near‐surface inversions of the Arctic and Antarctic. We find, using a fully coupled Earth system model, that the underlying surface warms despite the GHG addition exerting negative ERF and cooling the troposphere in the vicinity of the GHG increase. This unique radiative forcing and thermal response is facilitated by the high stability of the polar winter atmosphere, which inhibit thermal mixing and amplify the impact of surface radiative forcing on surface temperature. These findings also suggest that strategies to exploit negative ERF via injections of short‐lived GHGs into inversion layers would likely be unsuccessful in cooling the planetary surface. [ABSTRACT FROM AUTHOR]

Marine cold air outbreaks (MCAOs) are large-scale events in which cold air masses are advected over open ocean. It is well-known that these events are linked to the formation of polar lows and other mesoscale phenomena associated with high wind speeds, and that they therefore in some cases represent a hazard to maritime activities. However, it is still unknown whether MCAOs are generally conducive to higher wind speeds than normal. Here this is investigated by comparing ocean near-surface wind speeds during MCAOs in atmospheric reanalysis products with different horizontal grid spacings, along with two case-studies using a convection-permitting numerical weather prediction model. The study regions are the Labrador Sea and the Greenland-Iceland-Norwegian (GIN) Seas, where MCAOs have been shown to be important for air-sea interaction and deep water formation. One of the main findings is that wind speeds during the strongest MCAO events are higher than normal and higher than wind speeds during less severe events. Limited evidence from the case-studies suggests that reanalyses with grid spacings of more than 50 km underestimate winds driven by the large ocean-atmosphere energy fluxes during MCAOs. The peak times of MCAOs usually occur when baroclinic waves pass over the regions. Therefore, the strong wind episodes during MCAOs generally last for just a few days. However, MCAOs as defined here can persist for 50 days or more. [ABSTRACT FROM AUTHOR]

Polar Regions are experiencing environmental changes at unprecedented rates. These changes can spread throughout entire food webs from lower trophic levels to apex predators. As many top predators forage over large areas, these indirect effects may be associated with large-scale patterns of climate variability. Using global climate indices that are known to impact the Southern Ocean ecosystem (the El Niño Southern Oscillation and Antarctic Oscillation Indices) we assessed their efficacy to predict variation in the demographic parameters of Antarctic seabirds. First, we used a long-term dataset on adult survival (estimated from capture-mark-recapture data) and reproduction of Antarctic petrel Thalassoica antarctica, from the largest known breeding colony (Svarthamaren, Dronning Maud Land) and examined whether large-scale oceanographic fluctuations impact survival and reproduction. Second, we conducted an exhaustive literature review to determine whether the effects of large-scale environmental variability on Antarctic seabirds have a coherent fingerprint across the Antarctic continent and nearby islands. We found that most of the variation in both reproductive success, timing of hatching, and survival of Antarctic petrels can be accurately modeled using the two modes of large-scale climate variability in Antarctica. The literature review, combined with the results from our field study, suggests that while the anticipated trends in the global patterns of climatic variability will generally have detrimental effects on populations of top predators in the Southwest Atlantic, these conclusions cannot be extrapolated to all seabird populations in Antarctica without additional data. [ABSTRACT FROM AUTHOR]

The impact of observations on analysis uncertainty and forecast performance was investigated for austral spring 2010 over the southern polar area for four different systems (NRL, GMAO, ECMWF and Météo-France) at the time of the Concordiasi field experiment. The largest multi-model variance in 500 hPa height analyses is found in the southern sub-Antarctic oceanic region, where there are rapidly evolving weather systems, rapid forecast-error growth, and fewer upper-air wind observation data to constrain the analyses. The total impact of all observations on the model forecast was computed using the 24 h forecast sensitivity-to-observations diagnostic. Observation types that contribute most to the reduction of the forecast error are shown to be AMSU, IASI, AIRS, GPS-RO, radiosonde, surface and atmospheric motion vector observations. For sounding data, radiosondes and dropsondes, one can note a large impact on the analysis and forecasts of temperature at low levels and a large impact of wind at high levels. Observing system experiments using the Concordiasi dropsondes show a large impact of the observations over the Antarctic plateau extending to lower latitudes with the forecast range, with the largest impact around 50-70°S. These experiments indicate there is a potential benefit from using radiance data better over land and sea-ice and from innovative atmospheric motion vectors obtained from a combination of various satellites to fill the current data gaps and improve numerical weather prediction analyses in this region. [ABSTRACT FROM AUTHOR]

Global numerical weather prediction skill over polar areas is assessed, mostly based on the European Centre for Medium-Range Weather Forecasts (ECMWF) system but also theMet Office, Japan Meteorological Agency (JMA), Environment Canada andNational Centers for Environmental Prediction (NCEP) analysis data. Polar forecast verification against analyses shows a similar trend of forecast improvement over the past 12 years compared with improvements at lower latitudes. These improvements are presumably due to increased model resolution and model sophistication, improved data assimilation methods and increased observational data coverage and better data quality. By comparing ECMWF's real-time forecast skill changes against those from reforecasts initialized from reanalyses, it is possible to quantify how much of the improvement is from system improvements and how much is attributable to weather variability. Ensemble skill also improved over time and, again, consistently across latitudes. The quality of analyses serving for forecast verification and initialization has been investigated further. An intercomparison of The Observing system Research and Predictability Experiment (THORPEX) Interactive Grand Global Ensemble (TIGGE) analyses and forecasts revealed substantial differences for surface parameters, but also at lower levels in the troposphere, wheremost of the physical processes relevant to weather in the short-to-medium range take place over the poles. The differences between the TIGGE analyses were generally much larger than differences between members of the ECMWF4D-Var ensemble of analyses generated internally at ECMWF. This suggests that neither the multi-analysis approach nor ensemble data assimilation may represent polar analysis uncertainty properly. This is particularly visible at the surface and lower levels in the atmosphere. Forecast spread and error match much better north of 65°N where less atmospheric variability prevails along the entire forecast range, while in areas of significant synoptic activity the spread also appears too low. [ABSTRACT FROM AUTHOR]

High-latitude climate change is expected to increase the demand for reliable weather and environmental forecasts in polar regions. In this study, a quantitative assessment of the skill of state-of-the-art global weather prediction systems in polar regions is given using data from the THORPEX Interactive Grand Global Ensemble (TIGGE) for the period 2006/2007-2012/2013. Forecast skill in the Arctic is comparable to that found in theNorthernHemispheremidlatitudes. However, relative differences in the quality between different forecasting systems appear to be amplified in the Arctic. Furthermore, analysis uncertainty in the Arctic is more of an issue than it is in the midlatitudes, especially when it comes to near-surface parameters over snow- and ice-covered surfaces. Using NOAA's reforecast dataset, it is shown that the changes in forecast skill during the 7-year period considered here can largely be explained by flow-dependent error growth, especially for themore skilful forecasting systems. Finally, a direct comparison between the Arctic and Antarctic suggests that predictions of mid-topospheric flow in the former region are more skilful. [ABSTRACT FROM AUTHOR]

Weather and climate directly influence ski season length, the quality of snow conditions, and skier visits. Inter-annual climate variability, which is expected to become more pronounced under future climate change, poses an increased risk for the ski tourism industry. Using a survey (n=2448), this study examines where and how far skiers in Ontario (Canada) are willing to travel if their ski resort was to temporarily or permanently close due to a lack of snow. The majority of respondents (≥59%) would travel to five key resorts in Ontario, with the largest share (≥27%) selecting Blue Mountain Resort. An additional 11-15% of respondents would leave Ontario, opting to travel to Quebec or the state of New York. Overall, this paper presents the first empirical evidence on the geographical patterns skiers may engage in as a result of marginal snow conditions, in addition to providing information on travel distance and time thresholds. This research is fundamental for assessing contemporary climate risk and can inform how future climate change could alter demand patterns in regional ski marketplaces. Future research needs are identified to further appraise the consequences and future viability of individual ski resorts in Ontario and the ski industry more generally. [ABSTRACT FROM AUTHOR]

One of the clearest predictions from the IPCC is that we can expect much less snow cover due to global warming in the 21st century, especially in the lower alpine areas. In alpine ecosystems, snow accumulation in depressions gives rise to distinct snow-bed vegetation types, assumed to play a key role in ecosystem function. A delayed plant phenology yields high-quality forage in late summer for wild and domestic herbivores. Yet, the mechanistic pathways for how declining snow may affect future performance of large herbivores beyond the effect of phenology remain poorly documented., Here, we link unique individual-based data on diet choice, habitat selection and performance of domestic sheep over a 10-year period to manually GPS-recorded spatial positions of snow cover in early summer (0·57% to 43·3% in snow beds on 1st of July) in an alpine ecosystem., Snowy winters gave a higher proportion of easily digestible herbs in the diet and a more variable use of snow-bed and meadow vegetation types resulting in faster growing lambs. These patterns were consistent between two density treatment levels although slightly more marked for diet at low density, suggesting that effects of simple mitigation efforts such as managing population numbers will be meagre., Our study thus yields novel insight into the strong impact of melting snow on ecosystem function in alpine habitats, which are likely to affect productivity of both domestic and wild ungulate populations. [ABSTRACT FROM AUTHOR]

We investigate how the ocean response to CO2 forcing affects hemispheric asymmetries in polar climate sensitivity. Intermodel comparison of Phase 5 of the Coupled Model Intercomparison Project CO2 quadrupling experiments shows that even in models where hemispheric ocean heat uptake differences are small, Arctic warming still exceeds Antarctic warming. The polar climate impact of this evolving ocean response to CO2 forcing is then isolated using slab ocean experiments in a state‐of‐the‐art climate model. Overall, feedbacks over the Southern Hemisphere more effectively dissipate top‐of‐atmosphere anomalies than those over the Northern Hemisphere. Furthermore, a poleward shift in ocean heat convergence in both hemispheres amplifies destabilizing ice albedo and lapse rate feedbacks over the Arctic much more so than over the Antarctic. These results suggest that the Arctic is intrinsically more sensitive to both CO2 and oceanic forcings than the Antarctic and that ocean‐driven climate sensitivity asymmetry arises from feedback destabilization over the Arctic rather than feedback stabilization over the Antarctic. Plain Language Summary: Anthropogenic greenhouse gas emissions impact climate globally, but nowhere more so than over the Arctic, a phenomenon known as polar amplification. Surprisingly, the climate response over the Antarctic is much more muted than the climate response over the Arctic, which has been attributed to the large uptake of heat over the Southern Ocean which cools the Southern Hemisphere. Here we show that a weaker climate response over the Antarctic is due, in part, to weaker intrinsic sensitivity to both greenhouse gas forcing and the state of the ocean. Even climate models with similar amounts of heat uptake into the deep ocean in both hemispheres warm more over the Arctic than the Antarctic. Furthermore, similar increases in winter season heat transport into the polar oceans in both hemispheres trigger more destabilizing climate feedbacks over the Arctic than the Antarctic. Therefore, greater climate change over the Arctic than the Antarctic can be expected even if ocean heat uptake or ocean heat transport changes are similar in both hemispheres. Key Points: The Arctic has greater intrinsic sensitivity to ocean state changes than the AntarcticThe ocean response triggers more destabilizing radiative feedbacks over the Arctic than the AntarcticPolar radiative feedbacks respond more to increased high‐latitude ocean heat convergence than to subpolar ocean heat uptake [ABSTRACT FROM AUTHOR]

A photograph is presented depicting the view of a snow on February 5, 2013 between Conistone and Kettlewell, North Yorkshire, England, along with a stratus cloud flowing through the Aire gap into Upper Wharfedale in the Yorkshire Dales.